The present invention relates to an illumination apparatus, a light modulation apparatus, a display apparatus, a projection-type display apparatus and a rear-projection television. More particularly, the invention relates to an illumination apparatus, a light modulation apparatus, a display apparatus, a projection-type display apparatus and a rear-projection television having reduced irregular illumination from a light source having a light distribution characteristic.
A conventional picture display apparatus such as a projection-type picture display apparatus and a direct-view liquid crystal display apparatus and so forth modulates light illuminated from a light source by a light modulation clement so as to display a picture. A liquid crystal device, a DMD (Digital Micro-mirror Device) and so on, for example, are known as light modulation elements.
The liquid crystal device utilizes properties such as optical rotatory power and double refraction, and is used together with a polarizing element to control the brightness of light passing through each pixel. The DMD includes movable micro-mirrors corresponding to the number of pixels, and controls light paths to change the brightness of light passing therethrough.
A white light lamp such as a high-pressure mercury lamp, a xenon lamp, and a metal halide lamp and so forth, for example, is generally used as the light source which illuminates the light modulation element. Drawbacks common to such white light lamps are that a large number of iced rays are emitted, i.e., heat is generated, and the size of the entire optical system is increased due to the lamp having a large size.
In addition, it is difficult to balance an amount of light among three primary colors of R (Red), G (Green) and B (Blue) in color separation by a dichroic mirror and in color synthesis by a dichroic prism, and a large number of components arc required for carrying out the color separation and the color synthesis. Thus, problems also exist such as a limitation in improvement of color reproductivity and an increase in the size of an apparatus.
In recent years, light-emitting elements such as a LED (Light-Emitting Diode), a LD (Laser Diode), an EL (Electro-Luminescence) element and so forth have been a focus of attention and developed actively. Such light-emitting elements have advantages, as compared with the xenon lamps and the metal halide lamps for example, in that they do not include components such as the infrared rays and ultraviolet rays, they are capable of performing monochromatic illumination of RGB (Red, Green and Blue), lighting control therefor is relatively easy, they have a fast response speed, and they do not rupture, for example.
On the other hand, the light-emitting elements have a disadvantage in that an amount of illumination by a single light-emitting element is small, so that a large number of light-emitting elements are required in a picture display apparatus having a large screen. In addition, the LED has a characteristic in which different a light intensity distribution is indicated normally for each angle of exit, generally known as a light distribution characteristic. As illustrated in FIG. 9, when there is an angle θ from the center of directions of the exit of light, for example, in the light distribution, the light intensity in directions of θ weakens in accordance with cos θ. Due to such a characteristic, irregularity or unevenness is generated in the distribution of a light amount on a surface of an object to be illuminated as an illumination target.
Heretofore, a number of inventions which utilize the LED, LD and so on as the illumination light source have been filed, although there are only few inventions that can solve the irregularity in the light amount distribution caused by the light distribution characteristic described above. For example, Japanese patent publication No. 2001-343706, Japanese patent registration No. 3585097, and Japanese patent publication No. 2002-244211 are known. Japanese patent publication No. 2001-343706 proposes a picture display apparatus in which light emitted from light source parts, structured of LEDs and coupling lenses, is caused to enter a light valve through a condenser lens and an integrator. Japanese patent registration No. 3585097 discloses a liquid crystal display apparatus and so on in which the irregular light amount distribution is reduced by combining a plurality of LEDs with a light guide body. Japanese patent publication No. 2002-244211 proposes an image projection apparatus which balances high light-use efficiency and a small optical system, by providing polarized light conversion elements, each converting light emitted from LEDs into polarized light, correspondingly to each of the LEDs.
The picture display apparatus proposed in Japanese patent publication No. 2001-343706 aims to cause the light emitted from the plurality of light sources to enter the light valve uniformly and effectively. However, there are drawbacks in that the number of components required is large, and miniaturization is limited.
The liquid crystal display apparatus disclosed in Japanese patent registration No. 3585097 directly irradiates diffusion light emitted from the light guide body onto a light modulation member, and as a result, it cannot establish matching between the NA (Numerical Aperture) of a projection leas and the NA of an illumination optical system. Therefore, there is a problem of low light-use efficiency, i.e., a screen becomes dark even if the light modulation member is brightly illuminated, for example, in the invention disclosed in Japanese patent registration No. 3585097.
The image projection apparatus disclosed in Japanese patent publication No. 2002-244211 aims to achieve light-use efficiency and miniaturization, although the irregularity in the light amount distribution is not discussed.
For the foregoing reasons, there is a need for an illumination apparatus and so on that effectively condenses light from the light source, suppresses the irregularity in the light amount distribution on the surface of the object to be illuminated as the illumination target, and achieves minaturization as well as thinness.
Meanwhile, in recent years, giving presentations utilizing a projector has been widely prevalent, due to the progress in miniaturization and weight saving of various types of mobile equipment, as typified by notebook type personal computers, and thus mobile equipment can be easily portable. In accordance with the prevalence of the presentation utilizing the projector, miniaturization and weight saving of the projector are also in progress. However, a light source lamp such as a halogen lamp and metal halide lamp and so forth normally used for the existing projector is relatively large-sized and heavy. Accordingly, the LED has also been brought to attention for the light source lamp as an alternative to the halogen lamp and the metal halide lamp and so forth.
Various proposals have been made for a projector apparatus including a projector type display apparatus, an image projection apparatus and so on, in which the LED is used as the light source.
For example, Japanese patent publication No. 2001-249400 discloses a projector apparatus structured of a light-emitting element array, a fly-eye lens, a relay lens, a liquid crystal panel, and a projection lens system. Japanese patent publication No. H11-32278 discloses a projector apparatus structured of a light-emitting element array, a micro-lens array, a reduction-optical device, a dichroic mirror, a two-dimensional micro deflecting mirror array, and a projection optical system. The image projection apparatus according to the Japanese patent publication No. 2002-244211 discussed above is structured of a light-emitting element array, a polarized light conversion element, a dichroic prism, a deflection beam splitter, a liquid crystal light valve, and a projection optical system.
When focusing on an illumination apparatus of the projectors described above, the invention disclosed in Japanese patent publication No. 2001-249400 causes light emitted from the light-emitting element to directly enter the fly-eye lens. The invention of Japanese patent publication No. H11-32278 shapes light emitted from the light-emitting element by the micro-lens array, although a width of a light flux is narrowed and the light is directly guided to the two-dimensional micro deflecting mirror array alter the shaping is performed.
As described above, generally in the light emitted from the LED, the intensity of emission is different for each of the angles of irradiation, as represented by lengths illustrated by arrows in FIG. 9, and such a distribution of the intensity is often called the light distribution characteristic. When the structures disclosed in Japanese patent publication No. 2001-249400 and Japanese patent publication No. H11-32278 are utilized, it is obvious that the light distribution characteristic of the LED appears as irregular illuminance on the liquid crystal panel, the two-dimensional micro deflecting mirror array and so on. For example, even when a LED of a shell type is used for a light source to increase directivity of the emitted light and to decrease divergence of the light so as to lower the influence of the light distribution characteristic, the NA of the fly-eye lens becomes too small, which means that the liquid panel as a light modulation device cannot be illuminated in its entirety.
The image projection apparatus disclosed in Japanese patent publication No. 2002-244211, as described above, aims to achieve light-use efficiency and miniaturization. However, irregular illuminance is not discussed therein
For the foregoing reasons, there is also a need for a display apparatus, a projection-type display apparatus and a rear-projection television that reduces the irregular illuminance on the light modulation device and effectively irradiates the light emitted from the light source on the entire light modulation device.